Electrolytic process for production of gaseous hydrogen chloride and aqueous alkali metal hydroxide

Abstract

Disclosed is a process for the production of gaseous hydrogen chloride and aqueous alkali metal hydroxide from brine, utilizing an electrolytic cell containing a hydroxyl ion producing cathode and a gaseous hydrogen chloride producing hydrogen-consuming gas anode. Brine is fed to the anolyte compartment of the cell while alkali metal hydroxide is removed from the catholyte compartment of the cell, and gaseous hydrogen chloride is removed from the gaseous side of the hydrogen-consuming gas anode.

What is claimed is: 
     
       1. A continuous process for the production of gaseous hydrogen chloride and aqueous alkali metal hydroxide in an electrolytic cell containing an anode, cathode, anolyte, catholyte, anolyte compartment, catholyte compartment and a diffusion barrier separating said anolyte and catholyte compartments, said barrier being selectively permeable to water and alkali metal ions and said anode being a gas diffusion anode having a liquid side in contact with said anolyte and a gaseous side opposite said liquid side, which process comprises the steps of: (a) feeding an aqueous alkali metal chloride solution as anolyte into said anolyte compartment;   (b) feeding a hydrogen-containing gas to the gaseous side of said gas diffusion anode;   
     
     
       (c) maintaining an electrical potential between said cathode and anode whereby; (1) alkali metal ions and water pass from the anolyte through the diffusion barrier into the catholyte;   (2) hydroxy ions are formed at said cathode which react with said alkali metal ions forming alkali metal hydroxide in said catholyte; and   (3) hydrogen is oxidized at said anode and reacts with chloride ions producing hydrogen chloride;   (d) withdrawing catholyte from said catholyte compartment, said catholyte comprising an aqueous solution of alkali metal hydroxide;   (e) maintaining the pressure on the gaseous side of said anode such that at least 50% by weight of said hydrogen chloride produced at said anode escapes said anode via the gaseous side of said anode as gaseous hydrogen chloride; and   (f) withdrawing from the gaseous side of said anode gaseous hydrogen chloride, said gaseous hydrogen chloride comprising at least 50% by weight of the total quantity of hydrogen chloride produced at said anode.   
     
     
       2. The process of claim 1 wherein said cathode is a gas diffusion cathode and an oxygen-containing gas is fed to the gaseous side of said gas diffusion cathode. 
     
     
       3. The process of claim 2 wherein said alkali metal chloride is sodium chloride and said alkali metal hydroxide is sodium hydroxide. 
     
     
       4. The process of claim 3 wherein the electrical potential between said anode and cathode is maintained in the range of 0.2 to 1.5 volts. 
     
     
       5. The process of claim 4 wherein (a) the concentration of sodium chloride in said anolyte is 1 to 5.5 molar;   (b) the concentration of sodium hydroxide in said catholyte is 5 to 40 weight percent; and   (c) the electrical potential between said cathode and anode is maintained at 0.4 to 0.8 volts.   
     
     
       6. The process of claim 5 wherein at least 90% by weight of the total quantity of hydrogen chloride produced at said anode is withdrawn from the gaseous side of said anode. 
     
     
       7. The process of claim 5 wherein at least 95% by weight of the total quantity of hydrogen chloride produced at said anode is withdrawn from the gaseous side of said anode. 
     
     
       8. A continuous process for the production of gaseous hydrogen chloride and aqueous alkali metal hydroxide in an electrolytic cell containing an anode, cathode, anolyte, catholyte, anolyte compartment, catholyte compartment and a diffusion barrier separating said anolyte and catholyte compartments, said barrier being selectively permeable to water and alkali metal ions and said anode being a gas diffusion anode having a liquid side in contact with said anolyte and a gaseous side opposite said liquid side, which process comprises the steps of: (a) feeding an aqueous alkali metal chloride solution as anolyte into said anolyte compartment;   (b) feeding a hydrogen-containing gas to the gaseous side of said gas diffusion anode;   (c) maintaining an electrical potential between said cathode and anode whereby: (1) alkali metal ions and water pass from the anolyte through the diffusion barrier into the catholyte;   (2) hydroxy ions are formed at said cathode which react with said alkali metal ions forming alkali metal hydroxide in said catholyte; and   (3) hydrogen is oxidized at said anode and reacts with chloride ions producing hydrogen chloride;     (d) withdrawing catholyte from said catholyte compartment, said catholyte comprising an aqueous solution of alkali metal hydroxide;   (e) maintaining the pressure on the gaseous side of said anode such that at least 90% by weight of said hydrogen chloride produced at said anode escapes escapes said anode via the gaseous side of said anode as gaseous hydrogen chloride; and   (f) withdrawing from the gaseous side of said anode gaseous hydrogen chloride, said gaseous hydrogen chloride comprising at least 90% by weight of the total quantity of hydrogen chloride produced at said anode.   
     
     
       9. The process of claim 8 wherein said cathode is a gas diffusion cathode and an oxygen-containing gas is fed to the gaseous side of said gas diffusion cathode. 
     
     
       10. The process of claim 9 wherein said alkali metal chloride is sodium chloride and said alkali metal hydroxide is sodium hydroxide. 
     
     
       11. The process of claim 10 wherein the electrical potential between said anode and cathode is maintained in the range of 0.2 to 1.5 volts. 
     
     
       12. The process of claim 11 wherein (a) the concentration of sodium chloride in said anolyte is 1 to 5.5 molar;   (b) the concentration of sodium hydroxide in said catholyte is 5 to 40 weight percent; and   (c) the electrical potential between said cathode and anode is maintained at 0.4 to 0.8 volts.